A typical electron beam emitter includes a vacuum chamber with an electron generator positioned therein for generating electrons. The electrons are accelerated out from the vacuum chamber through an exit window in an electron beam. Typically, the exit window is formed from a metallic foil. The metallic foil of the exit window is commonly formed from a high strength material such as titanium in order to withstand the pressure differential between the interior and exterior of the vacuum chamber.
A common use of electron beam emitters is to irradiate materials such as inks and adhesives with an electron beam for curing purposes. Other common uses include the treatment of waste water or sewage, or the sterilization of food or beverage packaging. Some applications require particular electron beam intensity profiles where the intensity varies laterally. One common method for producing electron beams with a varied intensity profile is to laterally vary the electron permeability of either the electron generator grid or the exit window. Another method is to design the emitter to have particular electrical optics for producing the desired intensity profile. Typically, such emitters are custom made to suit the desired use.
The present invention includes an exit window for an electron beam emitter through which electrons pass in an electron beam. For a given exit window foil thickness, the exit window is capable of withstanding higher intensity electron beams than currently available exit windows. In addition, the exit window is capable of operating in corrosive environments. The exit window includes an exit window foil having an interior and an exterior surface. A corrosion resistant layer having high thermal conductivity is formed over the exterior surface of the exit window foil for resisting corrosion and increasing thermal conductivity. The increased thermal conductivity allows heat to be drawn away from the exit window foil more rapidly so that the exit window foil is able to handle electron beams of higher intensity which would normally burn a hole through the exit window.
In one embodiment, the exit window foil has a series of holes formed therein. The corrosion resistant layer extends over the holes of the exit window foil and provides thinner window regions which allow easier passage of the electrons through the exit window. The exit window foil is formed from titanium about 6 to 12 microns thick and the corrosion resistant layer is formed from diamond about 5 to 8 microns thick.
The present invention also includes an electron beam emitter including a vacuum chamber with an electron generator positioned within the vacuum chamber for generating electrons. The vacuum chamber has an exit window through which the electrons exit the vacuum chamber in an electron beam. The exit window includes an exit window foil having an interior and exterior surface with a series of holes formed therein. A corrosion resistant layer having high thermal conductivity is formed over the exterior surface and the holes of the exit window foil for resisting corrosion and increasing thermal conductivity. The layer extending over the holes of the exit window foil provides thinner window regions which allow easier passage of the electrons through the exit window.
In one embodiment, the electron beam emitter includes a support plate for supporting the exit window. The support plate has a series of holes therethrough which are aligned with holes of the exit window foil. In some embodiments, multiple holes of the exit window foil can be aligned with each hole of the support plate.
A method of forming an exit window for an electron beam emitter through which electrons pass in an electron beam includes providing an exit window foil having an interior and an exterior surface. A corrosion resistant layer having high thermal conductivity is formed over the exterior surface of the exit window foil for resisting corrosion and increasing thermal conductivity. A series of holes are formed in the exit window foil to provide thinner window regions where the layer extends over the holes of the exit window foil which allow easier passage of the electrons through the exit window.
In the present invention, by providing an exit window for an electron beam emitter which has increased thermal conductivity, thinner exit window foils are possible. Since less power is required to accelerate electrons through thinner exit window foils, an electron beam emitter having such an exit window is able to operate more efficiently (require less power) for producing an electron beam of a particular intensity. Alternatively, for a given foil thickness, the high thermal conductive layer allows the exit window in the present invention to withstand higher power than previously possible for a foil of the same thickness to produce a higher intensity electron beam. In addition, forming thinner window regions which allow easier passage of the electrons through exit window can further increase the intensity of the electron beam or require less power for an electron beam of equal intensity. Finally, the corrosion resistant layer allows the exit window to be exposed to corrosive environments while operating.